Insulating Question

[dogwood]

I have a one and one-half story house. I want to put some additional insulation behind the upstairs walls. The walls are 2x4, 8' tall, 16" on center, with sheetrock on the interior side. The voids between the 2x4's are filled with R-13 insulation. The new insulation is to be connected to the exposed backside of the 2x4's which I can get to in the attic space under the roof behind the walls. How do I connect insulation to the back edge of the 2x4's. I've always put insulation between studs, before never on them. There must be some common practice on how this is done. Thanks for your help.

Mike

 

[billb3]

I added 8 or 10 inch thick batts with the plastic wrapper to an attic knee wall (cape Cod).
I took one foot by 6 inch plywood and boards (scrap stuff) and screwed them about every two feet (they got further apart as time was progressing) sticking out of the 2x4 studs sides so I ended up with a whole bunch of tabs sticking out about one inch shy of the insulation batts and stapled plastic banding (the band they use on big cardboard boxes for shipping) to the tabs to hold the batts in place. I went an inch shy so they'd be tight enough so the batts would have less tendency to slide down.
Long staples stay in better.
I was going to go horizontal with the batts and just run some boards joist to rafter but I couldn't work with them collapsing.
(that's when I came up with tabs sticking out)
I could cut all the batts to the 4 and a half foot length and let them flop over while stapling the banding horizontally to the tabs
working my way like eating corn on the cob.

I ended up with small gaps between the batts that way so stuffed regular R13 strips in there afterwards.


I think I'd do rigid foam today with long screws.

 

[dogwood]

Bondo, I was trying to say there is nothing attached to the 1.5 inch edge of the 2x4's on the attic side. I need to connect the new insulation to the 1.5 inch edges of the 2x4's in some manner. It's standard wall construction, studs, insulation between the studs, a vapor barrier, and then sheetrock. Picture a house with rooms added upstairs with dormers. I can get to the "exposed" side of the the second floor addition's walls studs by crawling in the left-over attic space under the roof behind the walls.

Billb3, I've thought of going with rigid insulation and very well might, but was wondering if there were other ways of connecting in the pink stuff, as the rigid can be pricey. I'd like to get the walls up to R-26 or so.

Mike

 

[pen]

I still can't picture this. Real Pics would help.

I'm thinking you want to add insulation to your exterior walls by stuffing it down between the existing insulation and the dry wall from up in your attic? I think?

If so, fiberglass isn't the way to go as you'll never get it stuffed down there once you encounter wiring in the walls.

Perhaps blown in insulation?

I've seen a setup where guys drill a hole at the top of the wall and blow in insulation to fill. When I have seen it done though, it happened on the exterior of the house just before putting on new siding.


pen

 

[dogwood]

Pen, let me try one more explanation. Picture how a kid draws a house, a square with a triangle on top of it. I have a Cape Cod with this configuration. I added rooms and dormers in the attic space (inside the triangle representing the roof in a kid's picture). It was a big attic so I was able to fit in 8 ft walls. Smaller homes would have knee walls as Billb3 described. There, of course, was still left over unusable space behind the walls, and above the ceiling too for that matter. Before sheetrocking I insulated between the studs in these walls with 3.5" thick pink fiberglass insulation. I want to crawl back behind these upstairs walls and add more insulation to these walls. Since I've filled the voids between the studs already, I'm not sure how to connect any more insulation in.

Mike

 

[pyper]

I still can't picture this. Real Pics would help.

I get the impression that there is a wall and behind the wall is attic space. A knee wall. And for some reason, the wall is insulated, instead of the roof.

Do you have good access to the area? If you can get 4x8 sheets into the space, then you could tack rigid insulation to the backs of the studs.

 

[Highbeam]

I can totally picture the situation dogwood. One side of the wall is finished and the back side of that same wall is unfinished with great access since it's inside the attic. That's all that really matters. You've already filled the 2x4 wall bays with faced FG insulation and now want to add an additional 3.5 inches.

The pros would either remove the current insulation and then install new R-30 faced batts in the bays from the backside. OR they would add a new layer of unfaced 3.5 batts and attach it with that poly string stapled to the studs. It would be best practice to run the additional material horizontally so that long gaps and studs in the existing insulation are blocked off. Yes, you will compress the insulation slightly at the strings but only as needed to keep the second layer tight.

Be sure that the floor of this triangular attic space is also insulated as it is the ceiling to the room below. If It isn't, then you can use the removed R-13 batts as the first layer on the floor.

 

[dogwood]

Pyper, I can get 4x8 panels back there. I was hoping to find a less expensive alternative as I have approximately 160 linear feet of 8 ft. wall to insulate, not to mention the parts of the sidewalls of the dormers exposed in the remaining attic space. I've seen on TV where in unfinished basements, some type of soft insulation encased in a plastic wrap seems to be tacked onto concrete walls. I've not ever used this type product before but was thinking maybe someone know about a similar approach or product along those lines. I remember the 4'x8' foam panels I used under the house slab cost an arm and a leg and that was eighteen years ago. What type of foam panel would you recommend I check out to achieve an additional R-13? I need to cost this job out. Thanks for your help.

Mike

 

[dogwood]

You've got it exactly Highbeam. How often would you connect in the poly-string (I'll have to find out what that is exactly). Would you tie in the string on each stud for each width of horizontally rolled out fiberglass insulation, or could you attach it less often, say every other stud or so, or every couple widths?


I will be rolling out some additional insulation on the joists as well. Their voids are filled with R-30 now, if I recall correctly. Thanks so much.

Mike

 

[Highbeam]

I would hit every single stud between each bat. If the second layer of insulation is not tight against the first one then it becomes way less effective. The poly twine stuff that the insulation guys use comes out of a box and is the same stuff that you use at the HD to tie the red tag to your long lumber. It's thick like twine but white.

 

[dogwood]

Thanks again Highbeam. I'm on it. Noticed you live in WA. My wife grew up in Tacoma, and knew exactly where Buckley is. Met her when I lived in Monroe, north of Seattle, through the eighties. We've been in Virginia 20 years now but still miss the Pacific NW. Time does fly. Wonder if its still raining there every day this time of year. They still have that big fair in Puyallup every year. Appreciate your help, take care.

Mike

 

[Highbeam]

Rain most every day, grey skies, dark when I go to work and dark when I come home but at least it has been warm this month. The frogs were all croaking out in the pastures last night while we were soaking in the hot tub during the 45 degree weather. It rains a lot but that rain supports the trees, grass, and rivers that are so nice during the summer.

They still have the Puyallup fair, it's a big deal. I work down near the city limits of Puyallup so we can almost smell the food cooking during the fair.

Be sure not to strap the insulation down so hard that you compress the FG. You want it tight enough to stay against the old FG but not so tight that you compress it excessively since you lose R-value with compression. I expect that the strings can be pretty loose.

 

[pen]

Much clearer description the 3rd time!

Yea, do what highbeam said!

good luck

pen

 

[dogwood]

Thanks to you all. Another problem solved.

Mike

 

[pyper]

The folks at ORNL have an application that will tell you how much insulation is optimal for your location:

http://www.ornl.gov/~roofs/Zip/ZipHome.html

Where I live they suggest R-40 in the attic, which is 4x what you have now. If you need that much then the cheapest (unless your time is free), fastest alternative might be to take what you have out of the walls and put it on the ceilings and have someone spray foam on the walls.

That soft stuff in the plastic is an owens-corning product. I haven't seen it in a long time, but I put some in my attic. It's R-40 rolls. It's called "itchless" or something. It's fiberglass that's made with a different method, so it doesn't itch. Those bags get brittle with age and break down (at least mine did when I needed to move it this year), so you'd need some other way to hold it up.

Heat radiates equally in all directions, so you need the same on these walls as you do on the ceilings.

 

[Highbeam]

Funny, pyper said "cheap" and "spray foam" in the same sentence. I disagree that you need the same R-value in each direction, it is true that heat radiates in all directions but there is more than one form of heat transfer. The conduction and convection heavily favor a higher R-value in the ceilings.

 

[dogwood]

I'll take a look at the site Pyper mentioned and see what they recommend. I do have R-26 in the (2x8) walls downstairs and R-30 in the ceiling. I am trying to make the upstairs walls,, currently R-13, have the same value as the downstairs walls, and then will roll more insulation onto the ceiling joists. I don't know for sure what the point of diminishing returns is on ceiling and wall insulation is, but I'm fairly sure I'm not there yet. I wonder too, what the proper relation is between the R value of what should be in your ceiling versus your walls. I've always heard as you said, that ceiling insulation should be considerably higher in R value, but the exact relation is unknown to me. I've got a couple of older books on superinsulation from the mid 80's that may provide an answer, in addition to Pyper's recommended site. I'll look it up both places and post what I find out.

Mike

 

[pyper]

Funny, pyper said "cheap" and "spray foam" in the same sentence. I disagree that you need the same R-value in each direction, it is true that heat radiates in all directions but there is more than one form of heat transfer. The conduction and convection heavily favor a higher R-value in the ceilings.

Wheather it's cheaper or not depends on how much your time is worth... Framing out 160 linear feet to support insulation won't be free or fast.

There won't be any convection through walls or ceilings unless there are openings in them (by definition). If there are openings, then they should be sealed.

Conduction, just like radiation, is gravity-independent. It's true that heat-loss will be greater where the temperature differential is greatest. How much warmer is it on your ceiling than the mid-point (average) of your wall? Mine's warmer, but not all that much warmer. If it's 75F at the ceiling and 70F at the wall, and if it's 30F in the attic, then there's a 12% difference (in the differential). R-35 instead of R-40.

But if it's 140F in the attic, then it's only a 7% difference. R-37.

Heat seaks cold.

 

[dogwood]

Pyper's recommended DOE site recommended R-49 for the ceiling and R-13 for the walls for my area, near Roanoke, Virginia. My books on superinsulation recommended the ceiling insulation be double the R-value of the wall. Still haven't found the point of diminishing return in R-value yet. Imagine rising energy costs make it a bit of a moving target. "Tom in Maine" posting over in the Boiler Room Forum, has built walls with up to R-60 insulation, and has achieved very low energy usage especially considering his northerly location. His posts got me thinking I should revisit my own homes insulation. My costs were relatively low, taking into account the explosion in energy costs, prior to adding the living space in the attic with only R-13 in the walls. If anyone knows the point of diminishing return of wall and ceiling insulation thickness please chime in. Thanks.

Mike

 

[dogwood]

Pyper, I will be tying the new rolls to the existing framing as Highbeam suggested above, so at least will not have to re-frame. If I had to do it over again I would have used foam upstairs and down. It was cost prohibitive at the time of construction, since I did all the house building myself, and avoided any labor costs for insulating by putting in the pink stuff myself. I fully agree with you on the importance of sealing off any air leakage. I will go back and check for any potential air leakage points in the upstairs vapor barrier when I add the new insulation. I will be checking all the heat ducts and plenums likewise for leakage and will increase their insulation as well. As you point out the job will not be particularly pleasant or especially easy working in that cramped space. The labor is still free however, and I guarantee all my work for us 100% for life. Appreciate your input.

Mike

 

[ilateapex]

Go to pdhengineer.com and look up course M-4008 Energy Conservation. It gives a formula for payback of adding insulation on about page 6. Depending on energy costs in your area, it does not pay off as good as you may think. At least here where electric is around .08 per KWH. You can down load the pdf without having to pay for the class. You pay when you take the test.

Michael

 

[dogwood]

Thanks ilateapex. I'll check it out.

The link to the course is http://www.pdhengineer.com/courses/bd/M-4008.pdf if anyone else is interested.

Mike